1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to electrical wiring devices including protective features.
2. Technical Background
AC power is coupled to an electrical distribution system at a breaker panel. The breaker panel is disposed within a residence, commercial building or some other such facility. The breaker panel distributes AC power to one or more branch electric circuits installed in the structure. The electric circuits may typically include one or more receptacle outlets and may further transmit AC power to one or more electrically powered devices, commonly referred to in the art as load circuits. The receptacle outlets provide power to user-accessible loads that include a power cord and plug, the plug being insertable into the receptacle outlet. However, certain types of faults have been known to occur in electrical wiring systems. Accordingly, each electric circuit typically employs one or more electric circuit protection devices.
Electric circuit protective devices may be disposed within the breaker panel, receptacle outlets, plugs and the like. Both receptacle wiring devices and electric circuit protective wiring devices are disposed in an electrically non-conductive housing. The housing includes electrical terminals that are electrically insulated from each other. In particular, line terminals couple the wiring device to conductors coupled to the breaker panel. Load terminals are coupled to wiring that directs AC power to one or more electrical loads. Those of ordinary skill in the pertinent art will understand that the term “load” refers to an appliance, a switch, or some other electrically powered device.
Load terminals may also be referred to as “feed-through” terminals because the wires connected to these terminals may be coupled to a daisy-chained configuration of receptacles or switches. The load may ultimately be connected at the far end of this arrangement. Referring back to the device housing, the load terminals may be electrically connected to a set of receptacle contacts. The receptacle contacts are in communication with receptacle openings disposed on the face of the housing. This arrangement allows a user to insert an appliance plug into the receptacle opening to thereby energize the device.
Protective devices employ a circuit interrupter disposed between the line terminals and the load terminals. The circuit interrupter provides power to the load terminals under normal conditions, but breaks electrical connectivity when the protective device detects a fault condition in the load circuit.
There are several types of electric circuit protection devices including ground fault circuit interrupters (GFCIs), ground-fault equipment protectors (GFEPs), and arc fault circuit interrupters (AFCIs). This list includes representative examples and is not meant to be exhaustive. Some devices include both GFCIs and AFCIs. As their names suggest, arc fault circuit interrupters (AFCIs), ground-fault equipment protectors (GFEPs) and ground fault circuit interrupters (GFCIs) perform different functions.
An arc fault typically manifests itself as a high frequency current signal. Accordingly, an AFCI may be configured to detect various high frequency signals and de-energize the electrical circuit in response thereto. A ground fault occurs when a current carrying (hot) conductor creates an unintended current path to ground. A differential current is created between the hot/neutral conductors because some of the current flowing in the circuit is diverted into the unintended current path. The unintended current path represents an electrical shock hazard. Ground faults, as well as arc faults, may also result in fire.
A “grounded neutral” is another type of ground fault. This type of fault may occur when the load neutral terminal, or a conductor connected to the load neutral terminal, becomes grounded. While this condition does not represent an immediate shock hazard, it may lead to serious hazard. As noted above, a GFCI will trip under normal conditions when the differential current is greater than or equal to approximately 6 mA. However, when the load neutral conductor is grounded the GFCI becomes de-sensitized because some of the return path current is diverted to ground. When this happens, it may take up to 30 mA of differential current before the GFCI trips. Therefore, if a double-fault condition occurs, i.e., if the user comes into contact with a hot conductor (the first fault) when simultaneously contacting a neutral conductor that has been grounded on the load side (the second fault), the user may experience serious injury or death.
However, a protective device, like all electrical devices, has a limited life expectancy. This poses a problem in that when the device has reached end of life, the user may not be protected from the fault condition. End of life failure modes include failure of device circuitry, the circuit interrupter that opens (trips) the GFCI interrupting contacts, the relay solenoid that opens the GFCI interrupting contacts, and/or the solenoid switching device. Switching devices include thyristors such as the silicon controlled rectifiers (SCRs). An end of life failure mode can result in the protective device not protecting the user from the faults referred to above.
In one approach that has been considered, a test buttons is incorporated into a protective device to provide the user with a means for testing the effectiveness of the device. One drawback to this approach lies in the fact that if the user fails to use the test button, the user will not know if the device is functional. Even if the test is performed, the test results may be ignored by the user for various reasons.
What is needed is a protective device that denies power to the protected circuit when the device is non-protective. What is needed is a protective device that denies power to the protected circuit when the SCR is experiencing an end of life condition. What is needed is an auxiliary switch designed to have an improved reliability.